Abstract: This paper investigates if and how equity and efficiency could be reconciled when improving nitrogen-polluted groundwater of agricultural origin. This is achieved through comparing two pollution control programmes with respect to their costs, water quality impacts and correlation between abatement cost and polluting emissions. The fieldwork was done in a watershed, near the French Alps. It was carried out by economists in close relation with agronomists and hydrologists. The difficulty of the assessment of the environmental impact of the foreseen technological scenarios is overcome by developing an indicator of environmental effectiveness able to grasp the level of nitrate pollution of agricultural origin and to check whether the pollution control programmes are able to reach the given environmental target or not. The results show that it is only in the framework of a more flexible regulatory system that total abatement costs are reduced, and equity and efficiency reconciled,. This is due to the specific situation in agriculture the combination of various productions in every farm. This characteristic explains why the heterogeneity of the abatement costs is more significant within the firm (between production systems) rather than between firms.